Down-the-hole drill hammer

ABSTRACT

A down-the-hole drill hammer comprises a sleeve ( 46 ) which defines a cylinder in which a piston is reciprocable. A plurality of axially extending ribs are formed on the outer surface or the sleeve, and conduits are formed in at least one of the fibs for conveying compressed air or another drive fluid to ports in the sleeve, to operate the piston. This arrangement makes it possible to increase the effective diameter of the hammer as a percentage of the bit diameter, which is particularly useful in relatively small drill hammers.

BACKGROUND OF THE INVENTION

[0001] THIS invention relates to down-the-hole drills and particularly to a hammer arrangement therefor.

[0002] Down-the-hole (DTH) drilling is carried out with a drill-string-mounted hammer into which a bit is fitted. Compressed air is fed to a drill rig and passed through a rotating head through a number of hollow drill pipes connected end to end, with the hammer being connected to the final drill pipe, hence the term down-hole hammer. A piston in the hammer reciprocates, striking the bit and imparting percussive energy thereto, typically at between 15 to 30 times per second.

[0003] Until recently, down-the-hole drilling has been utilised for drilling holes larger than 70 mm in diameter (for example, 76 mm). For various reasons, it would be desirable to use down-the-hole drills to drill smaller diameter holes which up until now have mainly been drilled using top-hammer arrangements. However, as the hammer is made smaller in diameter, its manufacture becomes more difficult, and the power available from the hammer reduces, being related to the square of the piston diameter.

[0004] It is an object of the invention to provide a down-the-hole drill arrangement which can be adapted to the drilling of relatively small holes.

SUMMARY OF THE INVENTION

[0005] According to the invention there is provided a down-the-hole drill hammer comprising:

[0006] a sleeve defining a cylinder and defining at least one axially extending rib on the outer surface thereof;

[0007] a piston reciprocable within the cylinder and arranged to operate a bit percussively; and

[0008] at least one conduit formed in said at least one rib of the sleeve for conveying a drive fluid to one or more ports defined in the sleeve to operate the piston.

[0009] In one embodiment, said at least one rib in the sleeve is formed integrally with the sleeve, with said at least one conduit comprising a bore drilled in the sleeve.

[0010] The sleeve and the ribs thereof may be formed by machining or extrusion.

[0011] In other embodiments, the sleeve comprises an inner sleeve defining the cylinder within which the hammer is reciprocable, and an outer sleeve defining said at least one axially extending rib on the outer surface thereof, with said at least one conduit being defined between the inner and outer sleeves.

[0012] The inner sleeve may be formed from tubing or pipe, with the outer sleeve defining hollow axially extending ribs and being fitted about the inner sleeve.

[0013] The ribs may be defined by ridges or corrugations in the outer sleeve.

[0014] Alternatively, the outer sleeve defining the ribs may comprise a relatively thick-walled cylinder having axially extending slots formed in its inner surface adjacent the ribs, the inner sleeve fitting snugly within the outer sleeve to close off the slots, thereby to define the conduits.

[0015] The slots may be formed by machining or extrusion.

[0016] The drill hammer may include a shank reciprocable axially relative to the sleeve and having a first end within the sleeve engagable by the piston, and a second end extending beyond the sleeve and adapted to receive a bit.

[0017] The second end of the shank is preferably threaded to permit a bit to be screwed into position thereon.

[0018] The portion of the shank extending beyond the sleeve preferably has a diameter greater than the internal diameter of the sleeve, and preferably substantially equal to the maximum outer diameter of the sleeve.

[0019] In a variation of the invention, one or more of the conduits in the sleeve are designed to carry a flow of fluid to the bottom of the hole being drilled, said one or more conduits extending to the lower end of the wearsleeve and being ported to the exterior of the sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a sectional view of a down-the-hole drill hammer according to the invention;

[0021]FIG. 2 is a partial sectional view of the hammer of FIG. 1, showing the porting arrangements thereof in greater detail;

[0022] FIGS. 3 to 6 are cross sections through four different embodiments of wearsleeves of the hammer assembly illustrated in FIGS. 1 and 2;

[0023]FIG. 7 is a partial longitudinal section on the line 7-7 in FIG. 3;

[0024]FIGS. 8a to 8 d are sectional views corresponding to FIG. 1, showing the operating cycle of the hammer assembly; and

[0025]FIG. 9 is a partial longitudinal section of the bottom end of the hammer assembly, showing the chuck thereof in greater detail.

DESCRIPTION OF EMBODIMENTS

[0026]FIG. 1 shows a hammer assembly of a down-the-hole drill arrangement in longitudinal section. The hammer assembly comprises a hollow, generally cylindrical wearsleeve 10 within which is mounted a generally cylindrical piston 12. The piston 12 is reciprocable axially within the wearsleeve 10, and has a central axial through-bore 14.

[0027] The hammer assembly has a first, bottom end 16 and a second, top end 18. The terms “top” and “bottom” are used because, conventionally, down-the-hole drilling is carried out downwardly from the surface, so that the end of the hammer assembly which carries the bit will normally be lowermost. However, it should be appreciated that this is not necessarily the case.

[0028] At the bottom end 16 of the wearsleeve, a cylindrical shaft or shank 20 which is also reciprocable axially relative to the wearsleeve is provided. As best seen in FIG. 9, a first end 22 of the shank 20 is received within a chuck 64 at the bottom end of the wearsleeve and engages the lower end of the piston 12 in use. The shank has a second end 24 which is threaded or otherwise formed to engage a bit 26, and has an intermediate portion 28 with a diameter which is larger than the internal diameter of the wearsleeve 10, so that the bottom portion of the shank cannot retract into the wearsleeve.

[0029] The chuck 64 comprises a short length of pipe or tube of the same external diameter as the wearsleeve 10, which is welded to the bottom end of the wearsleeve 10 itself at 66. This is in contrast to conventional methods of threading the wearsleeve and the chuck and screwing them together, which weakens the walls of the chuck and wearsleeve in this region. This issue becomes critical with small diameter hammers, particularly those less than 40 mm in diameter. (Conventionally, the backhead 36 is also screwed into place at the top end of the wearsleeve, and welding can also be used here, with similar advantages.)

[0030] The welding of the components may be carried out by electron beam, TIG (Tungsten Inert Gas), MIG (Metal Inert Gas) or friction welding, for example.

[0031] The chuck 64 is formed with several axially extending splines 68 on its inner surface which engage complemental axial splines 70 on the outer surface of the shank 20. The inner end 22 of the shank is enlarged slightly relative to the splined portion thereof, and is fitted with a retaining ring 72 which holds the shank in the wearsleeve.

[0032] The shank 20 also has a central, axially extending through-bore 30 aligned with the bore 14 in the piston. A blower tube 32 extends from the upper end of the shank concentrically with the bores 30 and 14 and is received within the lower end of the bore 14 when the piston 12 approaches the shank 20. The bit 26 has a central, axial bore 34 aligned with the bore 30 in the shank 20.

[0033] Referring now to FIG. 2, at the top end of the hammer assembly is a backhead 36 which is connected in use to the bottom end of the lowermost drill pipe (not shown). The backhead 36 defines a central, axial conduit 38 which feeds compressed air via a check valve 40 and an air distributor assembly 42 into axially extending conduits in the wearsleeve 10 (see below). The respective conduits terminate in ports within the wearsleeve which are located so that the piston alternately opens and closes the respective ports as it reciprocates. The operating cycle of the hammer assembly is illustrated in FIGS. 8a to 8 d. (This aspect of the operation of the hammer assembly is generally conventional and is therefore not discussed in greater detail).

[0034] Referring now to FIGS. 3 to 6, four possible configurations of the wearsleeve 10 and the conduits therein are shown. In FIG. 3, the wearsleeve 10 is formed by milling hollow steel bar and has five equispaced axially extending ribs 44 on its outer surface. The ribs 44 define axially extending channels or valleys 46 between them through which material loosened by the bit 26 can be flushed upwardly, away from the bottom of the hole, by compressed air which is exhausted through the hole 34 in the bit. The outer diameter of the wearsleeve defined by the outer surfaces of the ribs 44 corresponds to, and is slightly less than, the diameter of the hole created by the bit 26.

[0035] Three of the ribs 44 each have three axially extending holes 48 drilled in them to define conduits for the compressed air provided by the distributor 42, and each set of holes 48 terminates in a respective port 50 located to be exposed when the piston is either uppermost or lowermost in its cycle, as the case may be. The sectional view of FIG. 7 illustrates the relative arrangement of a conduit defined by the holes 48 and its respective ports 50, and a further port 62.

[0036] Alternative arrangements of the wearsleeve 10 are shown in FIGS. 4, 5 and 6. In FIG. 4, the wearsleeve is also milled from hollow bar to define the ribs 44, but its wall thickness is generally constant. An inner sleeve 52 which is relatively thin-walled is fixed in position within the outer sleeve 54, and channels or slots 56 milled into the inside of each of the ribs 44 are sealed off by the inner sleeve 52 to define the conduits. The ports 50 are formed by drilling holes into the inner sleeve 52 as required, prior to insertion thereof into the outer sleeve.

[0037] In the arrangement of FIG. 5, the wearsleeve 10 comprises a relatively thick-walled inner sleeve 58 of uniform thickness, with a relatively thin-walled outer sleeve 60 fixed around it, with the ribs 44 being formed as “corrugations” of generally rectangular section in the sleeve 60 to define the conduits. The outer sleeve can be formed as an extrusion, or its “corrugations” could be formed in sheet metal which is then folded and welded into a tube. Again, the ports 50 are defined by drilling or cutting apertures into the inner sleeve 58 as required.

[0038] The arrangement of FIG. 6 is similar to that of FIG. 5, except that both the inner sleeve 58 and the outer sleeve 60 are formed of relatively thin walled material of uniform and generally equal thickness.

[0039] It will be appreciated that the above described embodiments of the wearsleeve 10 are purely exemplary, and that other embodiments are possible. What the embodiments have in common, however, is that they define a cylinder within which the piston 12 can reciprocate, with conduits for compressed air or other pressurised operating fluid being formed in axially extending ribs or ridges, on an outer surface of the wearsleeve.

[0040] In a variation of the invention, one or more of the conduits in the wearsleeve can be designed to carry a flow of fluid, typically water, to the bottom of the hole being drilled. This fluid suppresses dust from the drilling and in sufficient quantity can act as a flushing fluid to assist in carrying material loosened by the bit up the hole, in the valleys or channels between the ribs. In this embodiment, the relevant conduit(s) will not terminate in ports in the cylinder, but will extend to the lower end of the wearsleeve and be ported to the exterior of the wearsleeve.

[0041] By locating the conduits in the ribs, which serve the additional purpose of defining passages between them for the flushing of drilled material, the effective diameter of the hammer as a percentage of the bit diameter and thus the hole diameter is maximised. Conventional thinking has been limited to making the hammer diameter a fixed percentage of the hole diameter, for example 90% in the case of large hammers of greater than 200 mm diameter, and 80% to 85% of the hole diameter in relatively small hammers. Preliminary tests suggest that an increase in power of between 10% and 20%, typically in the region of 18%, is available from hammers designed using the principles of the invention.

[0042] A further advantage of the described ham mer assembly is that by providing a shank 20 which receives the bit 26 but which is a part of the hammer assembly itself and does not need to be replaced each time the bit is replaced, the size and therefore the cost of the consumable bit is substantially reduced, with a corresponding reduction in drilling costs. 

1-12. (cancelled).
 13. A down-the-hole drill hammer comprising: a sleeve defining a cylinder and defining a plurality of axially extending ribs on the outer surface thereof, the ribs defining passages between them for the flushing of drilled material; a piston reciprocable within the cylinder and arranged to operate a bit percussively; a shank reciprocable axially relative to the sleeve and having a first end within the sleeve engagable by the piston, and a second end extending beyond the sleeve and adapted to receive a bit; and at least one conduit formed in said at least one rib of the sleeve for conveying a drive fluid to one or more ports defined in the sleeve to operate the piston.
 14. A down-the-hole drill hammer according to claim 13 wherein said at least one rib in the sleeve is formed integrally with the sleeve, with said at least one conduit comprising a bore drilled in the sleeve.
 15. A down-the-hole drill hammer according to claim 14 wherein the sleeve and the ribs thereof are formed by machining or extrusion.
 16. A down-the-hole drill hammer according to claim 13 wherein the sleeve comprises an inner sleeve defining the cylinder within which the hammer is reciprocable, and an outer sleeve defining said at least one axially extending rib on the outer surface thereof, with said at least one conduit being defined between the inner and outer sleeves.
 17. A down-the-hole drill hammer according to claim 16 wherein the inner sleeve is formed from tubing or pipe, with the outer sleeve defining hollow axially extending ribs and being fitted about the inner sleeve.
 18. A down-the-hole drill hammer according to claim 17 wherein the ribs are defined by ridges or corrugations in the outer sleeve.
 19. A down-the-hole drill hammer according to claim 18 wherein the outer sleeve defining the ribs comprises a relatively thick-walled cylinder having axially extending slots formed in its inner surface adjacent the ribs, the inner sleeve fitting snugly within the outer sleeve to close off the slots, thereby to define the conduits.
 20. A down-the-hole drill hammer according to claim 19 wherein the slots are formed by machining or extrusion.
 21. A down-the-hole drill hammer according to claim 13 wherein the second end of the shank is threaded to permit a bit to be screwed into position thereon.
 22. A down-the-hole drill hammer according to claim 20 wherein the portion of the shank extending beyond the sleeve has a diameter greater than the internal diameter of the sleeve.
 23. A down-the-hole drill hammer according to claim 22 wherein the portion of the shank extending beyond the sleeve has a diameter substantially equal to the maximum outer diameter of the sleeve.
 24. A down-the-hole drill hammer according to claim 13 wherein one or more of the conduits in the sleeve are designed to carry a flow of fluid to the bottom of the hole being drilled, said one or more conduits extending to the lower end of the wearsleeve and being ported to the exterior of the sleeve. 